A conventional dispensing system for supplying heated adhesive (i.e., a hot-melt adhesive dispensing system) generally includes an inlet for receiving adhesive materials in solid or liquid form, a heater grid in communication with the inlet for heating and/or melting the adhesive materials, an outlet in communication with the heater grid for receiving the heated adhesive from the heated grid, and a pump in communication with the heater grid and the outlet for driving and controlling the dispensation of the heated adhesive through the outlet. One or more hoses may also be connected to the outlet to direct the dispensation of heated adhesive to adhesive dispensing guns or modules located downstream from the pump. Furthermore, conventional dispensing systems generally include a controller (e.g., a processor and a memory) and input controls electrically connected to the controller to provide a user interface with the dispensing system. The controller is in communication with the pump, heater grid, and/or other components of the dispensing system, such that the controller controls the dispensation of the heated adhesive.
Conventional hot-melt adhesive dispensing systems typically operate at ranges of temperatures sufficient to melt the received adhesive and heat the adhesive to an elevated application temperature prior to dispensing the heated adhesive. In order to ensure that the demand for heated adhesive from the gun(s) and module(s) is satisfied, the adhesive dispensing systems are designed with the capability to generate a predetermined maximum flow of molten adhesive. As throughput requirements increase (e.g., up to 20 lb/hour or more), adhesive dispensing systems have traditionally increased the size of the heater grid and the size of the hopper and reservoir associated with the heater grid in order to ensure that the maximum flow of molten adhesive can be supplied.
However, large hoppers and reservoirs result in a large amount of hot-melt adhesive being held at the elevated application temperature within the adhesive dispensing system. This holding of the hot-melt adhesive at the elevated application temperature may keep the hot-melt adhesive at a high temperature for only about 1 to 2 hours during maximum flow, but most conventional adhesive dispensing systems do not operate continuously at the maximum flow. To this end, adhesive dispensing systems typically operate with long periods of time where the production line is not in use and the demand for molten adhesive is zero, or lower than the maximum flow. During these periods of operation, large amounts of hot-melt adhesive may be held at the elevated application temperature for long periods of time, which can lead to degradation and/or charring of the adhesive, negative effects on the bonding characteristics of the adhesive, clogging of the adhesive dispensing system, and/or additional downtime.
In order to avoid or reduce the amount of degradation caused in the adhesive, several conventional adhesive dispensing systems have included a standby mode. When activated, the standby mode turns off the heat energy applied by the components of the dispensing system, thereby reducing the temperature of the adhesive within the dispensing system. The standby mode is activated based on an input received at the controller from the gun or module, and this input requires the provision of one or more additional wires or cables extending from the gun or module back to the controller. This additional wiring can be unsightly and increases the risk of catching the wire connections onto surrounding structures during operation of the gun or module. Furthermore, the dispensing system generally requires a relatively lengthy (5-30 minute) warm-up time to return the adhesive in the dispensing system back to the elevated application temperature after the dispensing system has been in standby mode for a period of time. These additional delays in warming up the system are undesirable to end users. As a result, substantially all end users do not use the standby mode available in conventional adhesive dispensing systems when that standby mode is the only mechanism provided for avoiding degradation during long periods of inactivity of the adhesive dispensing system.
For reasons such as these, an improved hot-melt adhesive dispensing system, including a control process for further reducing degradation of the adhesive would be desirable.